The present invention relates to an apparatus and method of tuning and locking wavelength in a tunable laser. More particularly, this invention relates to a laser resonant cavity implemented with dispersion compensated acousto-optic tunable filter and wavelength-locking design by which the fast-tuning speed, stable wavelength, and power performance can be realized.
Most modern telecommunications systems are based on fiber optic transmission. The fiber optic networks offer both unprecedented capacity and the deployment flexibility needed to support a wide range of evolving and emerging broadband applications. Widely tunable lasers help to maximize existing fiber optic network resource. The ability to dynamically provision bandwidth provides the ability to move traffic from overcrowded channels to unused channels to meet the demands for Internet access. Tunable laser is also a key prerequisite as networks move towards full mesh-based optical networks where light paths can be set up and changed quickly and easily.
The main features of an ideal tunable laser for such applications can be summarized as follows: wide tuning range covering C and/or L band (about 1530 nanometers to about 1610 nanometers), small footprint, fast tuning speed (in submilliseconds) between any two ITU grids, long-term performance stability (over 25 years of operation), highly reliable under severe work conditions, low electrical power consumption, low cost, and high manufacturbility.
Market penetration of tunable lasers is inhibited by the limitations of existing tunable lasers. The current tunable laser systems can be classified into the three types: (1) systems that use mechanically movable intracavity elements such as diffraction gratings, prisms, etalons or MEMS (microelectromechanical systems) as the wavelength tuning elements; (2) systems with thermally tunable elements built into the cavity and wavelengths are selected through thermally heating or cooling the elements; and (3) systems employ nonmovable intracavity optical elements for tuning, which involves the use of magneto-optic, acousto-optic, and electro-optic elements to physically select the wavelength.
Tuning techniques that rely on mechanical adjustment of the angle of a grating or prism are very susceptible to the mechanical shock and vibration causing short-term and long-term performance instability. Therefore tunable lasers employing moving parts are not suitable for optical telecom applications. Thermal tuning is intrinsically slow, and therefore its applications are limited.
Among the technologies which are based on tuning wavelength physically, acousto-optic technology which has been used as tuning element due to its electronic tunability without moving parts, fast tuning speed, wide tuning ranges, and relative simplicity in implementation is a viable approach to meet the stringent requirements of tunable lasers for telecom applications as described above. By appropriately selecting the acousto-optical crystals and driving acoustic frequencies, a tunable laser can be designed for operation within a wide range of wavelength spectrum.
A problem with the existing design of tunable laser utilizing acousto-optic filter for application in fiber optic telecom network are: (1) unstable laser oscillating in Fabry-Perot type cavity due to uncompensated dispersion; (2) the configuration of wavelength locker makes it very difficult to assembly and was not miniaturized; (3) unstable wavelength locker performance.
To solve the problems in the prior art and to meet the requirements for fiber optic telecommunication as described above, a new design for a tunable laser system with improved performance, reliability, and manufacturability is needed.